This invention relates to mechanical systems for the transmission of torque and, more particularly, to a joint and a method of fabricating such joint between two tubular members which transmit a torque.
Mechanical members for the transmission of torque are found in a large variety of mechanical systems ranging from automobiles to aircraft. For example, such structure is found in the drive shaft of an automobile as well as in a drag link used in an automobile steering mechanism. Also, such structure may be found in the mechanism for positioning airflow surfaces in an aircraft.
In the construction of such torque drive units, it is frequently necessary to join together a plurality of members to form the drive unit. The joining of two mechanical members is accomplished by means of a joint which is so configured so as to be able to transmit the torque. Where possible, the members are of tubular construction so as to provide for a savings in weight. Advantageously, the joining together of the members is accomplished with the aid of some form of indentation, as by the use of teeth or axial slots or grooves, so as to insure the transmission of torque without a circumferential slipping between the two members.
In one form of construction, as illustrated in the U.S. Pat. No. 1,291,388 disclosing a torque joint in an automotive drive shaft, one of the members is provided with a solid core while the second member is of tubular construction. The tubular shaft is then swaged upon the core of the other member so as to provide grooves within the tubular member, the grooves of the tubular member being nested within the grooves of the core so as to provide for the transmission of torque.
In the joining of two tubular members in a situation where it is desired to provide for axial tension with slippage in the circumferential direction, by way of contrast to the torque joint, an inner rotating mandrel and outer rotating roller may be utilized to impress a circumferential groove within two overlapping cylindrical structures as is disclosed in the U.S. Pat. No. 2,233,471. Another method of joining two tubular structures in a rigid joint configured for both axial tension and torque transmission is the use of a magnetic pulse for developing a momentary intense force which deforms the material of the two members as is disclosed in the U.S. Pat. No. 2,976,907. Alternatively, a strong shock induced in a fluid transmitting medium surrounding the work pieces to be joined may be utilized as is disclosed in the U.S. Pat. No. 3,163,141. In yet one other form of construction which may be utilized with swaging, the magnetic pulse or the shock method of fabrication is found in U.S. Pat. No. 1,329,479 wherein a relatively thick wall innertube is placed in overlapping relationship with an outer cylindrical member of thin wall construction. The thick wall inner member serves the additional function of a mandrel since it is sufficiently strong to resist the forces of deformation of the outer cylindrical member against the inner member in forming a torque joint.
A problem arises in that none of the foregoing torque joints have construction features useful in the joining together of two thin wall tubular members with provisions for axial and circumferential grooves to provide for the transmission of force, respectively, in the circumferential and in the axial directions. Such a torque joint is most useful in the aeronautics industry wherein it is important to save weight in each of the members of a mechanism utilized in the transmission of torque. Thus, the use of thin wall tubular members joined together by a suitable joint is most desirable.